The field of the invention relates to bidirectional signal transmission over a single filter utilizing wavelength duplexing.
There are many instances where duplex communication is desirable over a single optical fiber. Dichroic filters have typically been used in conjunction with the fibers to distinguish between two wavelengths.
A "cold" dichroic coating has been directly applied to an end face of an optical fiber. This application is often characterized by poor adhesion of the coating. A "hot" coating is generally preferred over a "cold" coating because of its increased adhesion and durability. The preferred method has been impractical, however, due to the different thermal expansion coefficients between the fiber, the epoxy holding the fiber to its substrate, and the substrate. As the coated end face is cooled, the multi-layer dielectric dichroic coating usually becomes detached or the adhesion becomes so weakened causing it to become detached at a later time. The survival rate is small which results in both wasted time and material. "Cold" coatings typically have poor adhesion characteristics and are not as durable as "hot" coating. Both "hot" and "cold" MLD i.e., dichroic coatings have been examined.
Although a "cold" multi-layer dielectric dichroic coating can be applied to the fiber end face, the adhesion and durability is poor. Accordingly the dichroic surfaces often do not survive the alignment process.